Ion implantation is implemented in various steps in the semiconductor manufacturing process; for example, it is implemented during formation of the diffusion region of the source/drain of a MOS transistor and in the formation of a polysilicon gate electrode. For example, Japanese Kokai Patent Application No. Hei 9[1997]-213258 discloses a large current ion implantation device which can increase the beam current without degrading the device characteristics. Furthermore, Japanese Kokai Patent Application No. 2009-87603 discloses an ion implantation device which is capable of controlling the amount of ion implantation very precisely even when the divergence angle or the beam gradient of the ion beam changes.
Methods for processing wafers with an ion implantation device can be broadly classified as a batch method or a single-substrate method. FIG. 1(a) shows an overview of a batch-type ion implantation device; FIG. 1(b) shows an overview of a single-substrate type ion implantation device. As shown in FIG. 1(a), a batch-type ion implantation device has a disk 1 on which are formed pedestals that respectively retain multiple wafers W which have been transported thereto. Disk 1 is rotated at a high speed of, for example, 1200 rpm and disk 1 is scanned mechanically in the vertical direction V, according to the amount of an ion beam B with which it is to be irradiated, from a more or less perpendicular or at an oblique angle with respect to disk 1, thus performing ion implantation of the wafers W. This method is primarily employed with high-current implantation devices. In particular, with a high-current process the wafers W are exposed to extremely high temperature, so that the wafers W must be cooled or the resist pattern formed on the wafers will be deformed by the heat, causing degradation of or variation in the device characteristics. Therefore, disk 1 is connected to a heat exchanger 3 via pipes 2A, 2B; water that is heated by disk 1 passes through pipe 2A and is cooled by heat exchanger 3, and cooled water is supplied to disk 1 through pipe 2B to cool wafers W. In addition, a chiller capable of temperature adjustment can be used in place of a heat exchanger.
Furthermore, as shown in FIG. 1(b), a single-substrate ion implantation device has a platen 4 that supports a wafer W. With respect to wafer W retained on platen 4, ion implantation of said wafer W is performed by a scanning beam B that scans in the horizontal direction H and by mechanically controlling the scan in the vertical direction V of scanning beam B and platen 4. This method primarily is employed with medium-current implantation devices. As with the aforementioned disk, platen 4 is connected to a heat exchanger 3 via pipes 2A, 2B, and the wafer retained on platen 4 is cooled by cooling water or a gas.
For both the batch-type and the single-substrate type methods shown in FIGS. 1(a) and (b), the temperature (the heat exchange efficiency) of a wafer W is a critical factor in the functioning of the implantation device, but the ion implantation device is not provided with a system to continuously monitor the wafer temperature. With both the batch processing method and the single-substrate processing method the pedestal and the wafer W are tightly adhered, or the platen and the wafer W are tightly adhered, and a basic premise is that heat exchange takes place normally between them. However, cooling systems these become completely ineffective when the pedestal or platen deteriorates or when contaminants or particles adhere to the pedestal or platen, causing wafer contact defects and resulting in an insufficient heat exchange, and in some cases the occurrence of a large number of product defects may not be noticed for a long time.